Recently in manufacturing semiconductor devices, resist patterns have been required to be miniaturized enough to meet increased integration density and highly accelerated processing speed in LSIs. This requirement has led to design rules requiring quarter-micron- or finer-scale fabrication rather than half-micron-scale fabrication, which the design rules formerly required. For the purpose of advancing the miniaturization, researchers are making studies on photosensitive resins and light sources for exposure. For example, since conventional light for exposure such as visible light or near UV light (wavelength: 400 to 300 nm) cannot fully satisfy the design rules requiring finer fabrication, it is studied to use practically radiation of shorter wavelength such as X-rays, electron beams and far UV light emitted from a KrF excimer laser (248 nm), an ArF excimer laser (193 nm) or the like. On the other hand, there are also various studies on the photosensitive resin composition. However, hitherto, the miniaturization has mainly depended upon improvement of the exposure light source and the exposure method, and hence cannot have been satisfyingly advanced only by improving the photosensitive resin composition.
In view of that, a new method for miniaturizing resist patterns is studied from a very different viewpoint. Specifically, a method is disclosed in which a resist pattern formed by the conventional method is covered afterward with a layer of even thickness so as to thicken the pattern and thereby to decrease the diameter of contact holes and/or the width of lines among the ridges in the resist pattern (Patent document 1 and 2). However, in the disclosed method, there is room for improvement on the covering layer. That is, when the resist pattern is subjected to the etching procedure after covered with the layer, the layer can be so etched unfavorably that the resultant transferred pattern has a line width and/or a contact hole diameter not so miniaturized as expected. In order to avoid this problem, it is desirable that the covering layer have enough etching resistance.    [Patent document 1] Japanese Patent Laid-Open No. 2008-275995    [Patent document 2] Japanese Patent Laid-Open No. 2008-102348